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Document handling of StorageDead.

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This commit is contained in:
Camille GILLOT 2023-05-31 17:28:24 +00:00
parent e11e4081df
commit f74695b010
1 changed files with 15 additions and 0 deletions
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15
compiler/rustc_mir_transform/src/const_prop.rs
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@ -889,6 +889,21 @@ impl<'tcx> MutVisitor<'tcx> for ConstPropagator<'_, 'tcx> {
StatementKind::StorageLive(local) => {
Self::remove_const(&mut self.ecx, local);
}
// We do not need to mark dead locals as such. For `FullConstProp` locals,
// this allows to propagate the single assigned value in this case:
// ```
// let x = SOME_CONST;
// if a {
// f(copy x);
// StorageDead(x);
// } else {
// g(copy x);
// StorageDead(x);
// }
// ```
//
// This may propagate a constant where the local would be uninit or dead.
// In both cases, this does not matter, as those reads would be UB anyway.
_ => {}
}
}